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BEGIN(5)
NAME
  BEGIN - start a transaction block

SYNOPSIS
  BEGIN [ WORK | TRANSACTION ]

  INPUTS

  WORK

  TRANSACTION
       Optional keywords. They have no effect.

  OUTPUTS

  BEGIN
       This signifies that a new transaction has been started.

  NOTICE: BEGIN: already a transaction in progress
       This indicates that a transaction was already in progress.  The
       current transaction is not affected.

DESCRIPTION
  By default, PostgreSQL executes transactions in unchained mode (also known
  as ``autocommit'' in other database systems).	 In other words, each user
  statement is executed in its own transaction and a commit is implicitly
  performed at the end of the statement (if execution was successful,
  otherwise a rollback is done).  BEGIN initiates a user transaction in
  chained mode, i.e., all user statements after BEGIN command will be
  executed in a single transaction until an explicit COMMIT [commit(5)],
  ROLLBACK [rollback(5)], or execution abort. Statements in chained mode are
  executed much faster, because transaction start/commit requires significant
  CPU and disk activity. Execution of multiple statements inside a
  transaction is also required for consistency when changing several related
  tables.

  The default transaction isolation level in PostgreSQL is READ COMMITTED,
  where queries inside the transaction see only changes committed before
  query execution. So, you have to use SET TRANSACTION ISOLATION LEVEL
  SERIALIZABLE just after BEGIN if you need more rigorous transaction
  isolation. In SERIALIZABLE mode queries will see only changes committed
  before the entire transaction began (actually, before execution of the
  first DML statement in a serializable transaction).

  If the transaction is committed, PostgreSQL will ensure either that all
  updates are done or else that none of them are done. Transactions have the
  standard ACID (atomic, consistent, isolatable, and durable) property.

  NOTES

  Refer to LOCK [lock(5)] for further information about locking tables inside
  a transaction.

  Use COMMIT [commit(5)] or ROLLBACK [rollback(5)] to terminate a
  transaction.

USAGE
  To begin a user transaction:

  BEGIN WORK;

COMPATIBILITY
  SQL92

  BEGIN is a PostgreSQL language extension.  There is no explicit BEGIN
  command in SQL92; transaction initiation is always implicit and it
  terminates either with a COMMIT or ROLLBACK statement.

       Note: Many relational database systems offer an autocommit feature as
       a convenience.

  Incidentally, the BEGIN keyword is used for a different purpose in embedded
  SQL. You are advised to be careful about the transaction semantics when
  porting database applications.

  SQL92 also requires SERIALIZABLE to be the default transaction isolation
  level.

Index for Section 5

Alphabetical listing for B

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